1. Field of the Invention
This invention refers to a novel method to overcome the pile-up effect in a scintillation detection system, particularly in a scintillation counter. It also refers to a device to carry out said method. Generally spoken, this invention relates to a method and a device for detecting scintillation occurrences. The invention may find its application in a scintillation counter, particularly in counting X-ray or gamma radiation, and in the field of nuclear medicine.
2. Description of the Prior Art
It is known that in measurements of electromagnetic X-ray radiation or gamma radiation using a scintillation crystal, one of the most important causes of error is an effect known as pile-up effect. While the error due to such a pile-up effect is negligible at low counting rates, it increases as the radiation beam increases until it interferes with the measurement at high counting rates.
As is known, the energy applied to a scintillation crystal by an X-ray or gamma photon is returned in the form of flashes of light. These flashes of light are conventionally converted into current pulses in a photomultiplier, and the said pulses extinguish themselves in a period of time which is in the order of microseconds. The so-called pile-up effect occurs whenever a new pulse is detected in the scintillator crystal and photo multiplier arrangement before the previous pulse has become extinguished. Naturally, the incidence of this effect is correlated to the counting rate. Hence the probability of its occurrance is all the greater the higher the pulse rate is.
In the field of nuclear medicine, the problem of the pile-up effect is particularly serious, since the spectrometry precision of the incident radiation conditions the scintigraphy results with scintillation chambers, i.e. the method by which radiactivity distribution maps are obtained. In fact, the pileup effect also causes spatial distortion and a significant worsening of the image resolution.
Scintillation chambers known to-date to obtain scintigraphies are frequently equipped with devices to off-set the pile-up effect. In the majority of cases these devices are based on the principle of executing the derivative before (from) the original signals. This principle makes it possible to remove only a limited and inconstant part of the contribution due to the pile-up effect, or to disregard the piled-up pulses, thereby reducing the efficiency of the system.